Convert seconds to hours, minutes, seconds

Question

How can I convert seconds to hours, minutes and seconds?

show_time() {
  ?????
}

show_time 36 # 00:00:36
show_time 1036 # 00:17:26
show_time 91925 # 25:32:0         


        

Answer 1

Using dc:

$ echo '12345.678' | dc -e '?1~r60~r60~r[[0]P]szn[:]ndZ2>zn[:]ndZ2>zn[[.]n]sad0=ap'
3:25:45.678

The expression ?1~r60~r60~rn[:]nn[:]nn[[.]n]sad0=ap does the following:

?   read a line from stdin
1   push one
~   pop two values, divide, push the quotient followed by the remainder
r   reverse the top two values on the stack
60  push sixty
~   pop two values, divide, push the quotient followed by the remainder
r   reverse the top two values on the stack
60  push sixty
~   pop two values, divide, push the quotient followed by the remainder
r   reverse the top two values on the stack
[   interpret everything until the closing ] as a string
  [0]   push the literal string '0' to the stack
  n     pop the top value from the stack and print it with no newline
]   end of string, push the whole thing to the stack
sz  pop the top value (the string above) and store it in register z
n   pop the top value from the stack and print it with no newline
[:] push the literal string ':' to the stack
n   pop the top value from the stack and print it with no newline
d   duplicate the top value on the stack
Z   pop the top value from the stack and push the number of digits it has
2   push two
>z  pop the top two values and executes register z if the original top-of-stack is greater
n   pop the top value from the stack and print it with no newline
[:] push the literal string ':' to the stack
n   pop the top value from the stack and print it with no newline
d   duplicate the top value on the stack
Z   pop the top value from the stack and push the number of digits it has
2   push two
>z  pop the top two values and executes register z if the original top-of-stack is greater
n   pop the top value from the stack and print it with no newline
[   interpret everything until the closing ] as a string
  [.]   push the literal string '.' to the stack
  n     pop the top value from the stack and print it with no newline
]   end of string, push the whole thing to the stack
sa  pop the top value (the string above) and store it in register a
d   duplicate the top value on the stack
0   push zero
=a  pop two values and execute register a if they are equal
p   pop the top value and print it with a newline

An example execution with the stack state after each operation:

    : 
?   : 12345.678
1   : 1, 12345.678
~   : .678, 12345
r   : 12345, .678  # stack is now seconds, fractional seconds
60  : 60, 12345, .678
~   : 45, 205, .678
r   : 205, 45, .678  # stack is now minutes, seconds, fractional seconds
60  : 60, 205, 45, .678
~   : 25, 3, 45, .678
r   : 3, 25, 45, .678  # stack is now hours, minutes, seconds, fractional seconds

[[0]n]  : [0]n, 3, 25, 45, .678
sz  : 3, 25, 45, .678  # '[0]n' stored in register z

n   : 25, 45, .678  # accumulated stdout: '3'
[:] : :, 25, 45, .678
n   : 25, 45, .678  # accumulated stdout: '3:'
d   : 25, 25, 45, .678
Z   : 2, 25, 45, .678
2   : 2, 2, 25, 45, .678
>z  : 25, 45, .678  # not greater, so register z is not executed
n   : 45, .678  # accumulated stdout: '3:25'
[:] : :, 45, .678
n   : 45, .678  # accumulated stdout: '3:25:'
d   : 45, 45, .678
Z   : 2, 45, 45, .678
2   : 2, 2, 45, .678
>z  : 45, .678  # not greater, so register z is not executed
n   : .678  # accumulated stdout: '3:25:45'

[[.]n]  : [.]n, .678
sa  : .678  # '[.]n' stored to register a
d   : .678, .678
0   : 0, .678, .678
=a  : .678  # not equal, so register a not executed
p   :   # accumulated stdout: '3:25:45.678\n'

In the case of 0 fractional seconds:

    : 3, 25, 45, 0  # starting just before we begin to print

n   : 25, 45, .678  # accumulated stdout: '3'
[:] : :, 25, 45, .678
n   : 25, 45, .678  # accumulated stdout: '3:'
d   : 25, 25, 45, .678
Z   : 2, 25, 45, .678
2   : 2, 2, 25, 45, .678
>z  : 25, 45, .678  # not greater, so register z is not executed
n   : 45, .678  # accumulated stdout: '3:25'
[:] : :, 45, .678
n   : 45, .678  # accumulated stdout: '3:25:'
d   : 45, 45, .678
Z   : 2, 45, 45, .678
2   : 2, 2, 45, .678
>z  : 45, .678  # not greater, so register z is not executed
n   : .678  # accumulated stdout: '3:25:45'

[[.]n]  : [.]n, 0
sa  : 0  # '[.]n' stored to register a
d   : 0, 0
0   : 0, 0, 0
=a  : 0  # equal, so register a executed
  [.] : ., 0
  n   : 0  # accumulated stdout: '3:35:45.'
p   :   # accumulated stdout: '3:25:45.0\n'

In case of a minutes value less than 10:

    : 3, 9, 45, 0  # starting just before we begin to print

n   : 9, 45, .678  # accumulated stdout: '3'
[:] : :, 9, 45, .678
n   : 9, 45, .678  # accumulated stdout: '3:'
d   : 9, 9, 45, .678
Z   : 1, 9, 45, .678
2   : 2, 1, 9, 45, .678
>z  : 9, 45, .678  # greater, so register z is executed
  [0]   : 0, 9, 45, .678
  n     : 9, 45, .678  # accumulated stdout: '3:0' 
n   : 9, .678  # accumulated stdout: '3:09'
# ...and continues as above

EDIT: this had a bug where strings like 7:7:34.123 could be printed. I have modified it to print a leading zero if necessary.